Despite all his passion for welfare reform, the real reason Iain Duncan Smith has resigned as work and pensions secretary is that his reforms have failed (see resignation letter). The immediate focus is on PIP (personal independence payments). The introduction of this benefit has not generated the savings that the government expected. In fact, more people have been given it than expected and the average payout is higher than expected (see BBC report). The introduction of PIP was slowed to try and implement it properly and avoid the number of successful appeals, as was the case with Employment Support Allowance (ESA). There are still many people waiting to be reassessed. It's not going to be easy for the new work and pensions secretary to get this budget under control. I suspect Stephen Crabb has a recognition from George Osbourne that he can't.